Geometrical characterization of inkjet-printed conductive lines of nanosilver suspensions on a polymer substrate

The effect of droplet/substrate interactions on the geometrical characteristics such as shape and morphology of as-printed conductive lines of nanosilver suspensions was investigated by varying the surface energy, substrate temperature and droplet spacing. With a plasma surface treatment using a mixture of C4F8 and O2 gases, various surface wettability conditions were obtained that could produce desired droplet diameters on the substrate from 30 μm to 70 μm. The substrate temperature varied from room temperature to 75 °C, and ink droplets ejected from a 30 μm nozzle were printed with various overlaps from 10% to 60%. When printed at room temperature, continuous lines are not formed due to line instability issues such as merging of neighboring droplets and line bulges. By heating the substrates, continuous lines without bulges could be obtained on the relatively hydrophobic substrate because the heat flux from the substrate enhances the evaporation rate of the solvent. The coffee ring effect in the droplets and lines is more enhanced as the substrate temperature increases. This effect is weaker in the lines than in the single droplets due to less edge length in the lines. Under appropriate conditions, well-defined continuous lines could be printed without coffee rings.